Zebrafish are commonly used in biological research because they are model organisms. Wikipedia defines a model organism as “a non-human species that can be studied to understand biological phenomena, with the expectation that any discoveries made… will provide insight into the workings of other organisms.”

In a recently published study, Fernando Casares and his colleagues at the Spanish National Research Council, describe how they’ve engineered zebrafish to develop autopods instead of fins.

An autopod is the furthest most point from the body in a limb’s structure. The development of autopods, “a precursor to hands, feet and paws”, is controlled by the hoxd13 gene. While zebrafish have the hoxd13 gene, they don’t have it in sufficient quantities to produce fully formed limbs.

In Casares’ study zebrafish were Casares’ project’s aim wasn’t to engineer fish with limbs, but rather to confirm findings from the fossil record; that limbsdeveloped from fins. By overexpressing the hoxd13 gene within the zebrafish, Casares’ project provides concrete evidence that the hoxd13 gene played a key role in the evolution of limbs.injected with extra copies of the hoxd13 gene to see whether any of them would replicate the gene on their own. After a day some zebrafish did replicate copies of the gene and began developing autopods in place of fins. Unfortunately they weren’t around long enough to put them to good use... They all died within four days.